This invention is directed to new methods for stereospecifically preparing [(1-optionally substituted aryl)- or (1-optionally substituted heteroaryl)]-2-substituted ethyl-2-amines, having chirality at the 2-position.
The invention is directed also to new intermediates that are useful for preparing substituted ethyl-2-amines.
The substituted ethyl-2-amines, and intermediate compounds therefor, are useful as intermediates in the synthesis of cardiovascular agents, including antihypertensive agents, anti-ischemic agents, cardioprotective agents which ameliorate ischemic injury or myocardial infarct size consequent to myocardial ischemia, and antilipolytic agents which reduce plasma lipid levels, serum triglyceride levels, and plasma cholesterol levels.
For example, the substituted ethyl-2-amines are useful as intermediates in the preparation of antihypertensive and anti-ischemic heterocyclyl adenosine derivatives and analogues as disclosed in U.S. Pat. No. 5,364,862. They are useful also in the preparation of N9-cyclopentyl-substituted adenine derivatives reported to be adenosine receptor ligands, and to be useful in treating cardiovascular conditions such as hypertension, thrombosis and atherosclerosis, and also in treating central nervous system conditions comprising psychotic conditions such as schizophrenia, and convulsive disorders such as epilepsy, as disclosed in U.S. Pat. No. 4,954,504. They are useful also in the preparation of N-6 and 5xe2x80x2-N substituted carboxamidoadenosine derivatives which have beneficial cardiovascular and antihypertensive activity as reported in U.S. Pat. No. 5,310,731.
Stereospecific preparation of chiral optionally substituted heteroaryl-2-substituted ethyl 2-amines by reaction of heteroaryl anions with 2-substituted ethylene oxides, and subsequent stereospecific conversion of the resulting chiral ethyl alcohol to the amine has been reported by Spada et al., in U.S. Pat. No. 5,364,862.
Facilitation of acidolytic cleavage reactions, for example the removal of various protecting groups, in the presence of electrophilic scavengers has been reported. Deprotection of NG-mesitylene-2-sulfonylarginine is reported by Yajima et al., Chem. Pharm. Bull. 26 (12) 3752-3757 (1978). Removal of the protecting group of O-benzyl serine, threonine, and tyrosine, and deprotection of Ne-benzyloxycarbonyllysine is reported by Kiso et al., Chem. Pharm. Bull. 28 (2) 673-676 (1980). Deprotection procedures for the p-toluenesulfonyl and p-methoxybenzenesulfonyl groups from the Nim function of histidine is reported by Kitagawa et al., Chem. Pharm. Bull. 28 (3) 926-931 (1980).
The present invention is directed to methods for stereospecifically preparing [(1-optionally substituted aryl)- or (1-optionally substituted heteroaryl)]-2-substituted ethyl-2-amines, having chirality at the 2-position, comprising reacting a 2-amino-2-substituted ethyl alcohol, having chirality at the 2-position, with an [(optionally substituted aryl)- or (trihalomethyl) sulfonyl]-halide or anhydride in the presence of a base to form an [(N-arylsulfonyl)- or (N-trihalomethylsulfonyl)]-2-substituted aziridine having chirality at the 2-position.
As used above, and throughout the description of this invention, the following terms, unless otherwise indicated, shall be understood to have the following meanings:
xe2x80x9cArylxe2x80x9d means phenyl or naphthyl.
xe2x80x9cOptionally substituted arylxe2x80x9d means an aryl group which may be substituted with one or more aryl group substituents. Examples of aryl group substituents include alkyl, alkoxy, amino, aryl, heteroaryl, trihalomethyl, nitro, carboxy, carboalkoxy, carboxyalkyl, cyano, alkylamino, halo, hydroxy, hydroxyalkyl, mercaptyl, alkylmercaptyl, and carbamoyl. Preferred aryl group substituents include halo, hydroxy, alkyl, aryl, alkoxy, trihalomethyl, cyano, nitro, and alkylmercaptyl.
xe2x80x9cHeteroarylxe2x80x9d means about a 4 to about a 10 membered aromatic ring structure in which one or more of the atoms in the ring is an element other than carbon, e.g., N, O or S. Examples of heteroaryl groups include pyridyl, pyridazinyl, pyrimidinyl, isoquinolinyl, quinolinyl, quinazolinyl, imidazolyl, pyrrolyl, furanyl, thienyl, thiazolyl, and benzothiazolyl. A preferred heteroaryl group is thienyl.
xe2x80x9cOptionally substituted heteroarylxe2x80x9d means that the heteroaryl group may be substituted by one or more heteroaryl group substituents. Examples of heteroaryl group substituents include alkyl alkoxy, alkylamino, aryl, carbalkoxy, carbamoyl, cyano, halo, heteroaryl, trihalomethyl, hydroxy, mercaptyl, alkylmercaptyl and nitro. Preferred heteroaryl group substituents include halo, hydroxy, alkyl, aryl, alkoxy, trihalomethyl, cyano, nitro, and alkylmercaptyl.
xe2x80x9cHalogenxe2x80x9d (xe2x80x9chaloxe2x80x9d, xe2x80x9chalidexe2x80x9d) means chlorine (chloro, chloride), fluorine (fluoro, fluoride), bromine (bromo, bromide) or iodine (iodo, iodide). xe2x80x9cAlkylxe2x80x9d means a saturated aliphatic hydrocarbon group which may be straight or branched and have about 1 to about 20 carbon atoms in the chain. Preferred alkyl groups may be straight or branched and have about 1 to about 10 carbon atoms in the chain. Lower alkyl means an alkyl group which may be straight or branched having about 1 to about 6 carbon atoms, such as methyl, ethyl, propyl or tert-butyl. Branched means that a lower alkyl group is attached to a linear alkyl chain.
xe2x80x9cAralkylxe2x80x9d means an alkyl group substituted by an aryl group. xe2x80x9cOptionally substituted aralkylxe2x80x9d means that the aryl group of the aralkyl group may be substituted with one or more aryl group substituents.
xe2x80x9cHeteroaralkylxe2x80x9d means an alkyl group substituted by a heteroaryl group. xe2x80x9cOptionally substituted heteroaralkylxe2x80x9d means that the heteroaryl group or the heteroaralkyl group may be substituted with one or more aryl group substituents.
xe2x80x9cElectrophilic scavengerxe2x80x9d means an agent that can have a promoting effect on acidolytic cleavage reactions, for example, as described by Yajima et al., Chem. Pharm. Bull. 26 (12) 3752-3757 (1978), Kiso et al., Chem. Pharm. Bull. 28 (2) 673-676 (1980), and Kitagawa et al., Chem. Pharm. Bull. 28(3)926-931 (1980).
An embodiment according to the invention is directed to the reaction of a 2-amino-2-substituted ethyl alcohol with a sulfonyl halide or anhydride, preferably in the presence of an aprotic organic solvent. Aprotic organic solvents which are suitable for the reaction include aprotic organic ethers, aromatic hydrocarbons, heteroaromatic hydrocarbons, aliphatic hydrocarbons, and aprotic organic amides. More particularly, examples of suitable aprotic organic solvents include diethyl ether, tert-butyl methyl ether, isopropyl methyl ether, diisopropyl ether, tetrahydrofuran, tetrahydropyran, and dioxan. In a special embodiment of methods according to the invention, the preferred aprotic organic solvent is tert-butyl methyl ether.
The reaction with the sulfonyl halide or anhydride takes place preferably at a temperature in the range of from about 25xc2x0 C. to about 90xc2x0 C.; more preferably from about 25xc2x0 C. to about 40xc2x0 C.
Suitable sulfonyl halides and anhydrides include phenyl-, tol-4-yl-, 2,4,6-trimethylphenyl-, 2,4-dimethylphenyl-, 4-methoxyphenyl-, 4-nitrophenyl-, 4-bromophenyl-, naphth-1-yl-, naphth-2-yl-, and trifluoromethyl-sulfonyl chloride and anhydride. In a special embodiment of methods according to the invention, a preferred sulfonyl chloride is p-toluenesulfonyl chloride (i.e., tol-4-yl sulfonyl chloride).
According to the invention, the reaction of the 2-amino-2-substituted ethyl alcohol with the sulfonyl halide or anhydride takes place in the presence of a base. Bases which are suitable for the reaction include aqueous alkali metal hydroxides, aqueous alkali metal carbonates, and aprotic organic amines. More particularly, examples of suitable alkali metal hydroxides include sodium hydroxide, potassium hydroxide, and lithium hydroxide; examples of suitable alkali metal carbonates include potassium carbonate, sodium carbonate, and cesium carbonate; and examples of suitable aprotic organic amines include triethylamine, diisopropyl ethyl amine, N-methylmorpholine, and pyridine. In a special embodiment of methods according to the invention, a preferred base is aqueous sodium hydroxide.
Another embodiment according to the invention is directed to the reaction of the [(N-arylsulfonyl)- or (N-trihalomethylsulfonyl)]-2-substituted aziridine having chirality at the 2-position, which is formed from the reaction of the 2-amino-2-substituted ethyl alcohol with the sulfonyl halide or anhydride, with an [(optionally substituted aryl)- or (optionally substituted heteroaryl)] lithium compound to form the lithium salt of an [(N-optionally substituted aryl)- or (N-trihalomethyl)sulfonyl]-1-[(optionally substituted aryl)- or (optionally substituted heteroaryl)]-2-substituted alkyl-2-amine having chirality at the 2-position. In a special embodiment of the invention, the lithium salt formed in the reaction is isolated as a solid.
Organolithium compounds may exist as tetramers, hexamers, and higher aggregates in hydrocarbon and ether solvents, as described, for example, by Carey, F. A., and Sundberg, Richard J., Advanced Organic Chemistry, Plenum Press, New York (2d ed. 1984), and Fraenkel et al., J Am. Chem. Soc. 102, 3345 (1980). Formation by methods according to the invention of such aggregates of the lithium salts, and the aggregates so-formed are contemplated by and included in the invention.
The reaction to form lithium salt takes place preferably in an aprotic organic solvent. Aprotic organic solvents which are suitable for the reaction include aprotic organic ethers, aliphatic hydrocarbons, and aromatic hydrocarbons. In a special embodiment of methods according to the invention, a preferred aprotic organic solvent is an aprotic organic ether and, more particularly, tert-butyl methyl ether.
The formation of the lithium salt takes place preferably at about xe2x88x9280xc2x0 C. to about 50xc2x0 C.; more preferably at about xe2x88x9240xc2x0 C. to about 50xc2x0 C.
Yet another embodiment according to the invention is directed to the treatment of the lithium salt of an [(N-optionally substituted aryl)- or (N-trihalomethyl)sulfonyl]-1-[(optionally substituted aryl)- or (optionally substituted heteroaryl)]-2-substituted alkyl-2-amine having chirality at the 2-position with one or more strong acids in the presence of an electrophilic scavenger. This treatment takes place preferably at a temperature range of about 45xc2x0 C. to about reflux.
Strong acids which are suitable for the treatment include methanesulfonic acid, trifluoroacetic acid, trifluoromethanesulfonic acid, trichloromethane sulfonic acid, trichloroacetic acid, sulfuric acid, hydrochloric acid, hydrobromic acid, and phosphoric acid. In a special embodiment of the invention, the treatment takes place preferably in a mixture of strong acids; more preferably in a mixture of methanesulfonic acid and trifluoroacetic acid.
Electrophilic scavengers which are suitable for the treatment include anisole, thioanisole, diphenyldisulfide, phenylbenzylsulfide, trimethoxybenzene, m-cresol, and 1,2-ethanediol. In a special embodiment according to the invention, a preferred electrophilic scavenger is thioanisole.
A preferred embodiment according to the invention is a method for preparing a compound of Formula I, 
wherein
* indicates a chiral carbon atom,
R1 is optionally substituted aryl, or optionally substituted heteroaryl; and
R3 is optionally substituted alkyl, optionally substituted aryl, optionally substituted aralkyl, optionally substituted heteroaryl, or optionally substituted heteroaralkyl,
comprising reacting a compound of Formula II 
with a compound of Formula III
R2xe2x80x94SO2xe2x80x94Rxe2x80x2xe2x80x83xe2x80x83Formula III
wherein
Rxe2x80x2 is halo or OSO2R2; and
R2 is optionally substituted aryl, or trihalomethyl,
in the presence of a base to form an aziridine compound of Formula IV. 
A further preferred embodiment of the present invention is the method of preparing a compound of Formula I wherein R1 is optionally substituted heteroaryl; more preferably wherein R1 is 3-chlorothien-2-yl.
Another further preferred embodiment of the invention is the method for preparing the compound of Formula I wherein R3 is alkyl; more preferably wherein R3 is ethyl.
Another preferred embodiment according to the invention is a method for preparing a compound of Formula I, comprising reacting the aziridine of Formula IV with a compound of formula Lixe2x80x94R1 to form a lithium compound of Formula V, 
or an aggregate thereof.
Another preferred embodiment according to the invention is a method for preparing a compound of Formula I, comprising treating the lithium compound of Formula V with a strong acid or mixture of strong acids in the presence of an electrophilic scavenger.
Preferred embodiments according to the invention are illustrated in Scheme I. 
If it is necessary or desirable to prevent cross-reaction between chemically active substituents (for example, any aryl or heteroaryl group substituents) during the reactions according to the invention, the substituents may be protected by standard blocking groups which may be subsequently removed or retained, as required, by known methods, to afford the desired product. (See, for example, Green, Protective Groups in Organic Synthesis, Wiley, New York (1982).) Selective protection or deprotection also may be necessary or desirable to allow conversion or removal of existing substituents, or to allow subsequent reaction to afford the final desired product.
The present invention is directed also to intermediates to [(1-optionally substituted aryl)- or (1-optionally substituted heteroaryl)]-2-substituted ethyl-2-amines.
A compound embodiment according to the invention is the [(N-arylsulfonyl)- or (N-trihalomethylsulfonyl)]-2-substituted aziridine having chirality at the 2-position, formed by the reaction of the of the 2-amino-2-substituted ethyl alcohol with the sulfonyl halide or anhydride according to the method of the invention. A preferred embodiment of said aziridine is the compound of Formula IV. A special embodiment of said aziridine includes 1-p-toluenesulfonyl-2(R)-ethylaziridine.
Another compound embodiment according invention is the lithium salt of an [(N-optionally substituted aryl)- or (N-trihalomethyl)sulfonyl]-1-[(optionally substituted aryl)- or (optionally substituted heteroaryl)]-2-substituted alkyl-2-amine having chirality at the 2-position formed by the reaction of the aziridine with an [(optionally substituted aryl)- or (optionally substituted heteroaryl)] lithium compound according to the method of the invention. A preferred embodiment of this lithium salt is the compound of Formula V. A special embodiment of the lithium salt is (R)-1-(3-chlorothien-2-yl)-2-butyltoluenesulfonamide lithium salt.